Aircraft employing turbo-machines enjoy higher performance than similar aircraft not equipped with turbo-machinery. For instance, turbojets provide significantly higher thrust at higher speeds and altitudes than the prior art engines. Modern turbojets include a compressor disc mounted on a shaft toward the forward end of the jet engine. The shaft also carries a turbine disc mounted on the aft end of the shaft. In operation, the compressor compresses rarified air drawn into the engine. Then, within a fuel mixing region of the engine, fuel nozzles inject fuel into the compressed air whereupon an igniter causes the air/fuel mixture to burn.
The now hot, and compressed, combustion gases flow through the turbine thereby forcibly turning the turbine and the shaft. In turn, the shaft turns the compressor thereby compressing more air. The partially expanded exhaust gases then escape via a converging exit nozzle to propel the aircraft forward. Because of the higher pressures and temperatures achieved via the compression of the air, the turbojet enjoys higher thrust than an engine without the turbine/compressor combination.
Many other turbo-machines enjoy similar advantages for similar reasons. However, turbo-machines are prone to vibration from the rotating parts (e.g. the compressor and turbine discs of a turbojet). The vibration arises because often the center of mass of each disc rotating assembly may be slightly displaced from the center of rotation. Moreover, the shaft may also suffer from slight misalignment and center of mass offsets too.
Thus, when the turbo-machine rotates, these imbalances cause the individual components (the compressor, the turbine, and the shaft) to vibrate. Differences between the levels of vibration of each part may aggravate the resulting movement of the machine. The vibration is typically transmitted through the aircraft structure generating corresponding noise and vibration in the cabin of the aircraft. Such vibration and noise often cause passenger and crew discomfort. Thus, a need exists to minimize the vibration and noise within the aircraft cabin causes by such engine vibrations.
Many other types of turbo-machines, beyond the turbojet engine discussed above, can suffer from the above described drawbacks. Therefore, it should be understood that references herein to turbo-machines includes any machine in which at least two parts rotate about a common shaft. Non-limiting examples of such rotating machinery include steam turbines, gas compressors, fluid pumps, gear trains, and turbochargers. Accordingly, a need exists to minimize the vibration and vibration induced movement generated by rotating machinery.